Method of producing magnetic materials



. A. L. DIXON El AL METHOD OF PRODUCING MAGNETIC MATERIALS June 15,1937.

Filed Dec. 7, 1933 FIG. /4 /5 Patented June 15, 1937 PATENT OFFICEMETHOD oF PnoDUcmG MAGNETIC MATERIALS Alfred L. Dixon, Hollywood, Ill.,and John V.

Davis, Daphne, Ala., assgnors to Western Electric Company, Incorporated,New York, N. Y., a' corporation of New York Application December 7,1933, Serial No. 701,254

8 Claims.

This invention relates to methods of proy ducing magnetic materials.

Objects of the invention are to provide magnetic materials of highpermeability and practical and effective methods of producing suchmaterials. A

In accordance with one embodiment of the invention, a ferromagneticmaterial is heattreated in a reducing atmosphere and during theheat-treatment a magnetic field is applied to the material whereby thepermeability of the material is greatly increased.

' Other objects and advantages will appear from the following detaileddescription taken in conjunction with the accompanying drawing, in whichFig. 1 is a sectional view of a device which may be used inpracticingthe invention.

Fig. 2 is a plan view of the device shown in Fig. l; and

Fig. 3 is a modied form of device of the type shown in Fig. 1.

In practicing the invention a piece of ferromagnetic material, as, for'instance, a piece of 5 iron of any suitable shape, such as 'a ring, bar

or vthe like, is placed in a fur-nace having a reducing atmosphere, suchashydrogen, and heated to slightly below the melting point of the iron,as, for instance, a temperature of 2700 F., and 30 the material ismaintained at this temperature for a period of about A24 hours. Itappears that y the hydrogen combines with some of the impurities in theiron, such asv sulphur, oxygen, nitrogen, carbon, etc., producingvolatile compounds 35 which are expelled from the iron and thus tends topurify the iron. rDuring this period the iron is in the gamma phase andit appears that the gamma crystals of the material are greatly increasedin size. The period of 24 hours during 40 which the material ismaintained at this high temperature is not critical, although the bestresults lare obtained by treating the material for approximately thisperiod.' The material is then cooled and it has been found that the rateof cooling is not critical, although the best results are obtained bycooling the material at a slow rate by allowing it to cool in thefurnace. When the material is cooled and passes through the A3transformation point, at a temperature of about 1652 F., it passes intotheealpha phase accompanied by a change in crystal structure. It appearsthat during this change certain strains are set up in the material whichimpair the magnetic properties of the material. kThe 55 material istherefore again heated to abtemperatu're just slightly below the A3transformation point as, for instance, a temperature of 1620 F.. in thecase of iron, and maintained at this tern- Y perature for a period ofabout 2 hours. This second heat-treatment is also preferably carried outin a hydrogen atmosphere and during this treatment the'material issubjected to the influence of a magnetic eld for the purpose ofincreasingthe permeability of the material. It has been found that ironwhich is heat-treated as described above, without the application of .amagnetic eld during the treating process, has a maximum permeability inthe neighborhood of 50,000; whereas, the same material when subjected tothe inuence of a magnetic field during the heat-treatment has a maximumpermeability of 100,000 to 150,000. In some cases permeabilities as highas 228,000 have been obtained by this process.

Referring now to the drawing, Figs. 1 and 2 show a device for applying amagnetic field to magnetic materials in ring form.V This devicevconsists of upper and lower plates 5 and 6 which have annular cut-outportions 1 and 8 which form an annular cavity or tunnel 9 when theplates are superposed. The plates 5 and 6 are provided with conductinginserts Il and l2. Inserts l2 are provided with a bore at their upperends and the inserts Il are provided with projections I3 which t intothe bores ofthe inserts l2 to make a conducting connection between theinserts in the upper and lower plates. The outer ends of the pins Il andI2 are connected by conductors I4 in such-a manner as to provide ahelical winding around the material in the annular cavity 9. The plates5 and 6 are preferably made of a refractory material to withstand thehigh temperatures in the furnace and are preferably provided withapertures l5 to provide access of the hydrogen in the furnace to -thematerial in the device. 'I'he material to be treated may be placed inthe-furnace in the device described at the beginning of the heattreatingoperation and leads I6 of the device may be connected to a source ofcurrent to provide a magnetic eld vfor `the material during the heattreatment. It is not essential that the magnetic field be maintainedduring the en- -tire heat-treatment and excellent results have beenobtained 'by applying the magnetic iield only during the secondheat-treatment, while the material is being heated for Several hoursslightly below the A3 transformation point. Preferably, however, themagnetic eld is applied during the entire second heat-treatment, thatis, while the material is being heated to a point slightly below the A3transformation point until it is cooled. y

As an illustration of a specific vexample of a method embodying theinvention, a ring of magnetic iron may be heated in a hydrogenatmosphere to 2700 F. for 24 hours and then cooled in the furnace. 'I'hematerial is then placed in a fixture such as shown in Fig. 1 and thematerial is again placed in the furnace and raised to a temperature ofapproximately 1620 F. and maintained at this temperature forapproximately two hours. I'he fixture has twelve turns thereon and analternating current of 60 cycles per minute and of 6 amperes is passedthrough the winding during the second heat treating operation. Due tothe fact that the eddy currents set up in the material by an alternatingcurrent prevent effective penetration of the magnetic eld when highfrequencies are used, a low frequency i'ield, preferably of 60 'cyclesper minute, is applied.

In some cases a field strength of approximately 6 oersteds has beenapplied to the material with excellent results. It has been found thatirnproved results may be had with various intensities of the magneticeld. Magnetic fields as low as l oersted, as well as magnetic fields ashigh as 15 oersteds,` improve the magnetic properties o f the material.

Fig. 13 illustrates a device which may be used for treating magneticmaterial in bar shape and comprises a tube I1 in which the material maybe inserted, having av winding IB thereon for subjecting the material toa magnetic eld.

After the iirst heat-treatment of the material, the material may bedistorted or worked into any suitable shape desired. The distorting orworking of the material will, of course. produce strains in the materialwhich will ailect its magnetic properties. These strains, however, areremoved in the second heat-treatment when the material is treated at a.temperature slightly below the A3 transformation point, and, therefore,material which has been worked after the first heattreatment may'. besubjected to the second heattreatment in the same manner as materialwhich has not been worked after the first heat-treatment.

, It will be understood that the nature and embodiments of the inventionherein described are merely illustrative and that many changes andmodifications may be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. A method of producing magnetic iron which comprises treating the ironat a temperature of the order of 1600 F. and subjecting the iron to avarying magnetic iield at substantially said temperature during theheat-treatment and maintaining said temperature and the application ofsaid magnetic iield for a period sufcient ito materially increase thepermeability of the ron.

2. A method of producing magnetic iron which comprises treating the ironin a reducing atmosphere at a temperature of the order of 2700" F.,

cooling the iron, treating the iron at a temperature of the order of1600 F. and subjecting the iron to a varying magnetic field during thesecond heat-treatment.

3. A method of producing magnetic iron which comprises heating the ironto a temperature 'of the order of 2700 F., maintaining said temperaturefor substantially twenty-four hours, cooling the iron, reheating theiron to a ltemperature of the order of 1620 F., maintaining saidtemperature for substantially two hours, subjecting the iron tothe'iniiuence of a magnetic iield during the second heat-treatment, andcooling the iron at a rate to provide an annealed product.

4. A method of producing magnetic iron which j comprises heating theiron to a temperature of the order of 2700 F., maintaining saidtemperature for substantially twenty-four hours, cooling the iron,working the ir'on, reheating the iron to a temperature of the order'of1620 F., maintaining said temperature for substantially two hours,subjecting the iron to the iniiuence of a magnetic field during thesecond heat-treatment, and cooling the iron at a rate to providev anannealed product.

5. A method of producing ferro-magnetic material which comprises heatingthe material at a high temperature but below its melting point in areducing atmosphere, maintaining this tem- `perature for a substantialperiod, cooling the material, reheating the material to a temperaturebelow the A3 transformation point, maintaining the material at thistemperature for a substantial period, and applying a magnetic iield tothe material during the second heat-treatment.

6. A method of producing ferro-magnetic material which comprises heatingthe material to a temperature slightly below the A3 transformation pointand substantially above the A2 transformation point and applying amagnetic ield to the material during vthe heating operation, andmaintaining substantially said temperature and the application of themagnetic field for a period to materially'increase the permeability ofthe iron.

' 7. A method of producing ferro-magnetic material which comprisesheating the material to a temperature slightly below the A3transformation point and substantially above the A2 transformation pointand applying a varying magnetic field to the material during the heatingoperation and maintaining the material in said temperature range andapplying said magnetic iield for a period suiiicient to materiallyincrease the permeability of the material.

8. A method of producing magnetic iron which comprises heating'the ironto a temperature of the order of 1620 F., maintaining lsaid temperaturefor a period sufficient to materially increase the permeability of theiron, subjecting the iron to the influence of a magnetic ileld duringthe heat treatment, and cooling the iron at a rate to provide anannealed product.

ALFRED` L. DIXON. JOHN' V. DAVI.

